Problem: Simplify the following expression: $x = \dfrac{n}{5} - \dfrac{n}{2}$
Solution: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $5$ and $2$ $\lcm(5, 2) = 10$ $ x = \dfrac{2}{2} \cdot \dfrac{n}{5} - \dfrac{5}{5} \cdot \dfrac{n}{2} $ $x = \dfrac{2n}{10} - \dfrac{5n}{10}$ $x = \dfrac{2n -5n}{10}$ $x = \dfrac{-3n}{10}$